Brain Mechanisms

The consociate modulator. Adams has developed a thought provoking and novel model. Its wide scope allows commentary from numerous points of view, but I will confine mine to the proposed consociate modulator in order to deal with it in detail.

The consociate modulator is viewed as being localized in the ventromedial nucleus of the hypothalamus. A concern that this immediately raises is whether the localization can be made precisely in this way. This is important inasmuch as further developments of the model attribute behavioral effects to afferents and efferents of this nucleus; It does not appear that existing evidence warrants this degree of localization since many of the results that implicate the medial hypothalamus in the control of aggressive behavior damage substantial tissue outside the ventromedial nucleus. Further, in a recent attempt to delimit the region involved in the modulation of intermale attack, mouse killing, and reactivity to an experimenter, the critical area was fairly diffuse in the rostromedial hypothalamus while in the posterior hypothalamus it appeared to be centered in the region between the ventromedial nucleus and the fornix (Albert and Wong 1978a).

With respect to the proposed connections of the consociate modulator, the circuit drawn connecting the cingulate cortex, hippocampus, and septum with the ventromedial nucleus seems quite shaky. Three experiments report no effect of cingulate cortex stimulation, either in terms of reactivity to the experimenter or of mouse killing (Brayley and Albert 1977, 1977a; Albert, Brayley, and Milner 1978). There does not appear to be substantial evidence for hippocampal efferents through the septum playing much of a direct role in the modulation of aggression. The septum itself, which contains these hippocampal efferents, is a relatively ineffective site for inducing increased aggression using lesions. The more effective site in this general area is ventral to the lateral septum along the medial edge of the rostral limb of the anterior commissure (Albert and Brayley 1979; Albert and Richmond 1975; Albert and Wong 1978b). Finally, there is little evidence that the lateral septum or the region ventral to the anterior septum modulates aggression by way of input to the ventromedial nucleus since the reactivity to the experimenter induced by medial hypothalamic lesions is suppressed by stimulation in the region of the septum (Brayley and Albert 1977).

Functionally, the consociate modulator is initially proposed to broadly regulate the tendency to behave defensively or submissively to a "familiar individual of the same or different species." However, the detailed development of the model is concerned primarily with intraspecific aggression. Existing evidence itself suggests that intraspecific aggression is modulated by the medial hypothalamus in the same way as an attack on a mouse (Albert and Wong 19788) Defensiveness, as manifested in increased reactivity to an experimenter, is modulated independently of the tendency to attack a mouse or another rat (Albert and Brayley 1979; Albert and Wong 1978a; Eclancher and Karli 1971; Panksepp 1971a). Because it appears that the medial hypothalamus modulates a broad spectrum of interspecific and intraspecific aggressive behavior. Adams's suggestion that the medial hypothalamus regulates defense-submission seems too limited. An alternative conceptualization is that the medial hypothalamus is one part of a neural system modulating the tendency to emit an attack and the tendency to act defensively. The neural control of these two dimensions of behavior appears to overlap in the medial hypothalamus, but whether there is an integrated control of these two dimensions of behavior is not clear (Albert and Wong 1978a, 1978b).